Method for treating a bone

ABSTRACT

A method provides a void creation device including an expandable structure adapted to undergo expansion in the cancellous bone volume of a bone selected for treatment. The expandable structure has at least one dimension so that the expandable structure will assume a predetermined shape and size when substantially expanded that compacts only a first volume of the cancellous bone volume to form a void, leaving a second volume of the cancellous bone volume substantially uncompacted by the expandable structure. A filling material is placed within the void through the percutaneous access path.

RELATED APPLICATIONS

This application is a divisional of co-pending U.S. patent applicationSer. No. 09/884,365, filed Jun. 19, 2001, entitled “Method for Treatinga Vertebral Body,” which is a continuation of U.S. patent applicationSer. No. 08/911,805, filed Aug. 15, 1997 (now abandoned), which is acontinuation-in-part of U.S. patent application Ser. No. 08/871,114,filed Jun. 9, 1997 (now U.S. Pat. No. 6,248,110), which is acontinuation-in-part of U.S. patent application Ser. No. 08/659,678,filed Jun. 5, 1996 (now U.S. Pat. No. 5,827,289), which is acontinuation-in-part of U.S. patent application Ser. No. 08/485,394,filed Jun. 7, 1995 (now abandoned), which is a continuation-in-part ofU.S. patent application Ser. No. 08/188,224, filed Jan. 26, 1994 (nowabandoned), entitled, “Improved Inflatable Device For Use In SurgicalProtocol Relating To Fixation Of Bone.”

FIELD OF THE INVENTION

The invention relates to the treatment of bone conditions in humans andother animals.

BACKGROUND OF THE INVENTION

When cancellous bone becomes diseased, for example, because ofosteoporosis, avascular necrosis, or cancer, the surrounding corticalbone becomes more prone to compression fracture or collapse. This isbecause the cancellous bone no longer provides interior support for thesurrounding cortical bone.

There are 2 million fractures each year in the United States, of whichabout 1.3 million are caused by osteoporosis alone. There are also otherbone disease involving infected bone, poorly healing bone, or bonefractured by severe trauma. These conditions, if not successfullytreated, can result in deformities, chronic complications, and anoverall adverse impact upon the quality of life.

U.S. Pat. Nos. 4,969,888 and 5,108,404 disclose apparatus and methodsfor the fixation of fractures or other conditions of human and otheranimal bone systems, both osteoporotic and non-osteoporotic. Theapparatus and methods employ an expandable body to compress cancellousbone and provide an interior cavity. The cavity receives a fillingmaterial, which hardens and provides renewed interior structural supportfor cortical bone.

The better and more efficacious treatment of bone disease that thesePatents promise can be more fully realized with improved systems andmethods for making and deploying expandable bodies in bone.

SUMMARY OF THE INVENTION

The invention provides a method that provides a void creation deviceincluding an expandable structure adapted to undergo expansion in thecancellous bone volume of a bone selected for treatment. The expandablestructure has at least one dimension so that the expandable structurewill assume a predetermined shape and size when substantially expandedthat compacts only a first volume of the cancellous bone volume to forma void, leaving a second volume of the cancellous bone volumesubstantially uncompacted by the expandable structure. A fillingmaterial is placed within the void through the percutaneous access path.

Features and advantages of the invention are set forth in the followingDescription and Drawings, as well as in the appended Claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a plan view of a probe that carries an expandable structurethat embodies features of the invention;

FIG. 2 is a lateral view, partially broken away and in section, of alumbar vertebra;

FIG. 3 is a coronal view of the lumbar vertebra, partially cut away andin section, shown in FIG. 2;

FIG. 4 is a lateral view of the lumbar vertebra shown in FIGS. 2 and 3,partially cut away and in section, with the expandable structure shownin FIG. 1 deployed by transpedicular access when in a substantiallycollapsed condition;

FIG. 5 is a coronal view of the transpedicular access shown in FIG. 4,partially cut away and in section;

FIG. 6 is a lateral view of the lumbar vertebra shown in FIG. 4, afterexpansion of the expandable structure shown in FIG. 1 to form a cavity;

FIG. 7 is a perspective view of one representative embodiment of anexpandable structure having a stacked doughnut-shaped geometry;

FIG. 8 is a view of another representative embodiment of an expandablestructure having an oblong-shaped geometry;

FIG. 9 is an elevation view of another representative embodiment of anexpandable structure showing three stacked structures and string-likerestraints for limiting the expansion of the bodies during inflation;

FIG. 10 is a perspective view of another representative embodiment of anexpandable structure having a kidney bean-shaped geometry;

FIG. 11 is a top view of another representative embodiment of anexpandable structure having a kidney bean-shaped geometry with severalcompartments formed by a heating element or branding tool;

FIG. 12 is a cross-sectional view taken along line 12-12 of FIG. 11;

FIG. 13 is a perspective, lateral view of a vertebral body, partiallybroken away to show the presence of an expandable structure, and alsoshowing the major reference dimensions for the expandable structure;

FIG. 14 is a dorsal view of a representative expandable structure havinga humpback banana-shaped geometry in use in a right distal radius;

FIG. 15 is a cross sectional view of the expandable structure shown inFIG. 14, taken generally along line 15-15 of FIG. 14;

FIG. 16 is a side view, with parts broken away and in section, of anexpandable structure having an enclosed stiffening member, to straightenthe structure during passage through a guide sheath into an interiorbody region;

FIG. 17 is a side view of the expandable structure shown in FIG. 16,after deployment beyond the guide sheath and into the interior bodyregion, in which the stiffening member includes a distal region having apreformed bend, which deflects the structure relative to the axis of theguide sheath;

FIG. 18 is a plan view of a sterile kit to store a single use probe,which carries an expandable structure of the type previously shown; and

FIG. 19 is an exploded perspective view of the sterile kit shown in FIG.18.

The invention may be embodied in several forms without departing fromits spirit or essential characteristics. The scope of the invention isdefined in the appended claims, rather than in the specific descriptionpreceding them. All embodiments that fall within the meaning and rangeof equivalency of the claims are therefore intended to be embraced bythe claims.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The preferred embodiment describes improved systems and methods thatembody features of the invention in the context of treating bones. Thisis because the new systems and methods are advantageous when used forthis purpose. It should be appreciated that the systems and methods asdescribed are not limited to use in the treatment of bones.

I. The Expandable Structure

FIG. 1 shows a tool 10, which includes a catheter tube 12 having aproximal and a distal end, respectively 14 and 16. The catheter tube 12includes a handle 18 near its proximal end 14 to facilitate gripping andmaneuvering the tube 12. The handle 18 is preferably made of a foammaterial secured about the catheter tube 12.

The distal end 16 carries an expandable structure 20. The structure 20is shown in FIG. 1 in a substantially collapsed geometry. Whensubstantially collapsed, the structure 20 can be inserted into theinterior of a bone, as will be described in greater detail later.

Generally speaking (and as will be demonstrated in greater detaillater), an animal bone includes an exterior formed from compact corticalbone, which encloses an interior volume of reticulated cancellous, orspongy, bone (also called medullary bone or trabecular bone). Whencollapsed, the structure 20 is deployed in the cancellous bone.

As will also be described in greater detail later, the structure 20,when expanded, compresses the cancellous bone and thereby creates aninterior cavity. The cavity is intended to receive a filling material,e.g., bone cement, which hardens and provides renewed interiorstructural support for surrounding cortical bone. The compaction ofcancellous bone also exerts interior force upon cortical bone, making itpossible to elevate or push broken and compressed bone back to or nearits original prefracture, or other desired, condition.

U.S. Pat. Nos. 4,969,888 and 5,108,404 disclose the use of expandablestructures for the fixation of fractures or other conditions of humanand other animal bone systems, both osteoporotic and non-osteoporotic.These Patents are incorporated herein by reference.

A. Material Selection for the Expandable Structure

The material of the expandable structure 20 can be selected according tothe therapeutic objectives surrounding its use. For example, materialsincluding vinyl, nylon, polyethylenes, ionomer, polyurethane, andpolyethylene tetraphthalate (PET) can be used. The thickness of thestructure is typically in the range of 2/1000ths to 25/1000ths of aninch, or other thicknesses that can withstand pressures of up to, forexample, 250-500 psi.

If desired, the material for the structure 20 can be selected to exhibitgenerally elastic properties, like latex. Alternatively, the materialcan be selected to exhibit less elastic properties, like silicone. Usingexpandable bodies with generally elastic or generally semi-elasticproperties, the physician monitors the expansion to assure thatover-expansion and wall failure do not occur. Furthermore, expandablebodies with generally elastic or generally semi-elastic properties mayrequire some form of external or internal restraints to assure properdeployment in bone. The use of internal or external restraints inassociation with expandable bodies used to treat bone is discussed ingreater detail in co-pending U.S. patent application Ser. No.08/485,394, filed Jun. 7, 1995, which is incorporated herein byreference.

Generally speaking, for use in treating bone, providing relativelyinelastic properties for the expandable structure 20, while not alwaysrequired, is nevertheless preferred, when maintaining a desired shapeand size within the bone is important, for example, in a vertebralstructure, where the spinal cord is nearby. Using relatively inelasticbodies, the shape and size can be better predefined, taking into accountthe normal dimensions of the outside edge of the cancellous bone. Use ofrelatively inelastic materials also more readily permits the applicationof pressures equally in a defined geometry to compress cancellous bone.

When treating bone, the choice of the shape and size of a expandablestructure 20 takes into account the morphology and geometry of the siteto be treated. The shape of the cancellous bone to be compressed, andthe local structures that could be harmed if bone were movedinappropriately, are generally understood by medical professionals usingtextbooks of human skeletal anatomy along with their knowledge of thesite and its disease or injury. The physician is also able to select thematerials and geometry desired for the structure 20 based upon prioranalysis of the morphology of the targeted bone using, for example,plain films, spinous process percussion, or MRI or CRT scanning. Thematerials and geometry of the structure 20 are selected to optimize theformation of a cavity that, when filled with bone cement, providesupport across the middle region of the bone being treated.

In some instances, it is desirable, when creating a cavity, to also moveor displace the cortical bone to achieve the desired therapeutic result.Such movement is not per se harmful, as that term is used in thisSpecification, because it is indicated to achieve the desiredtherapeutic result. By definition, harm results when expansion of thestructure 20 results in a worsening of the overall condition of the boneand surrounding anatomic structures, for example, by injury tosurrounding tissue or causing a permanent adverse change in bonebiomechanics.

As one general guideline, the selection of the geometry of theexpandable structure 20 should take into account that at least 40% ofthe cancellous bone volume needs to be compacted in cases where the bonedisease causing fracture (or the risk of fracture) is the loss ofcancellous bone mass (as in osteoporosis). The preferred range is about30% to 90% of the cancellous bone volume. Compacting less of thecancellous bone volume can leave too much of the diseased cancellousbone at the treated site. The diseased cancellous bone remains weak andcan later collapse, causing fracture, despite treatment.

Another general guideline for the selection of the geometry of theexpandable structure 20 is the amount that the targeted fractured boneregion has been displaced or depressed. The expansion of the structure20 within the cancellous bone region inside a bone can elevate or pushthe fractured cortical wall back to or near its anatomic positionoccupied before fracture occurred.

However, there are times when a lesser amount of cancellous bonecompaction is indicated. For example, when the bone disease beingtreated is localized, such as in avascular necrosis, or where local lossof blood supply is killing bone in a limited area, the expandablestructure 20 can compact a smaller volume of total bone. This is becausethe diseased area requiring treatment is smaller.

Another exception lies in the use of an expandable structure 20 toimprove insertion of solid materials in defined shapes, likehydroxyapatite and components in total joint replacement. In thesecases, the structure 20 shape and size is defined by the shape and sizeof the material being inserted.

Yet another exception lays the use of expandable bodies in bones tocreate cavities to aid in the delivery of therapeutic substances, asdisclosed in copending U.S. patent application Ser. No. 08/485,394,previously mentioned. In this case, the cancellous bone may or may notbe diseased or adversely affected. Healthy cancellous bone can besacrificed by significant compaction to improve the delivery of a drugor growth factor which has an important therapeutic purpose. In thisapplication, the size of the expandable structure 20 is chosen by thedesired amount of therapeutic substance sought to be delivered. In thiscase, the bone with the drug inside is supported while the drug works,and the bone heals through exterior casting or current interior orexterior fixation devices.

The materials for the catheter tube are selected to facilitateadvancement of the expandable structure 20 into cancellous bone. Thecatheter tube can be constructed, for example, using standard flexible,medical grade plastic materials, like vinyl, nylon, polyethylenes,ionomer, polyurethane, and polyethylene tetraphthalate (PET). Thecatheter tube can also include more rigid materials to impart greaterstiffness and thereby aid in its manipulation. More rigid materials thatcan be used for this purpose include stainless steel, nickel-titaniumalloys (Nitinol™ material), and other metal alloys.

B. Selection of Shape and Size for the Expandable Structure

As will also be demonstrated later, when relatively inelastic materialsare used for the structure 20, or when the structure 20 is otherwiseexternally restrained to limit its expansion prior to failure, apredetermined shape and size can be imparted to the structure 20, whenit is substantially expanded. The shape and size can be predeterminedaccording to the shape and size of the surrounding cortical bone 28 andadjacent internal structures, or by the size and shape of the cavitydesired to be formed in the cancellous bone 32.

In one embodiment, which is generally applicable for treating bonesexperiencing or prone to fracture, the shape and size of the structure20, when substantially expanded, can be designed to occupy at leastabout 30% of the volume of cancellous bone 32 in the interior volume 30.A structure 20 having a substantially expanded size and shape in therange of about 40% to about 99% of the cancellous bone volume ispreferred.

In another embodiment, which is applicable for treating bones havingmore localized regions of fracture or collapse caused, for example, byavascular necrosis, the shape and size of the structure 20 can bedesigned to occupy as little as about 10% of the cancellous bone volume.In this embodiment, the structure 20 is deployed directly at thelocalized site of injury.

The shape of the cancellous bone 32 to be compressed, and the presenceof surrounding local anatomic structures that could be harmed ifcortical bone were moved inappropriately, are generally understood bymedical professionals using textbooks of human skeletal anatomy, alongwith their knowledge of the site and its disease or injury. Thephysician is also able to select the materials and geometry desired forthe structure 20 based upon prior analysis of the morphology of thetargeted bone using, for example, plain films, spinous processpercussion, or MRI or CRT scanning. The materials and geometry of thestructure 20 are selected to create a cavity of desired size and shapein cancellous bone without applying harmful pressure to the outercortical bone or surrounding anatomic structures.

In some instances, it is desirable, when creating the cavity, to move ordisplace the cortical bone to achieve the desired therapeutic result.Such movement is not per se harmful, as that term is used in thisSpecification, because it is indicated to achieve the desiredtherapeutic result. By definition, harm results when expansion of thestructure 20 results in a worsening of the overall condition of the boneand surrounding anatomic structures, for example, by injury tosurrounding tissue or causing a permanent adverse change in bonebiomechanics.

II. Treatment of Vertebral Bodies

FIG. 2 shows a lateral (side) view of a human lumbar vertebra 22. FIG. 3shows a coronal (top) view of the vertebra 22. The vertebra 22 includesa vertebral body 26, which extends on the anterior (i.e., front orchest) side of the vertebra 22. The vertebral body 26 is in the shape ofan oval disk.

As FIGS. 2 and 3 show, the vertebral body 26 includes an exterior formedfrom compact cortical bone 28. The cortical bone 28 encloses an interiorvolume 30 of reticulated cancellous, or spongy, bone 32 (also calledmedullary bone or trabecular bone).

The spinal canal 36 (see FIG. 2), is located on the posterior (i.e.,back) side of each vertebra 22. The spinal cord 37 passes through thespinal canal 36. The vertebral arch 40 surrounds the spinal canal 36.Left and right pedicles 42 of the vertebral arch 40 adjoin the vertebralbody 26. The spinous process 44 extends from the posterior of thevertebral arch 40, as do the left and right transverse processes 46.

A selected expandable structure 20 can be inserted into bone inaccordance with the teachings of the above described U.S. Pat. Nos.4,969,888 and 5,108,404. For a given vertebral body 26, access into theinterior volume 30 can be accomplished, for example, by drilling anaccess portal 43 through either or both pedicles 42. FIG. 4 shows asingle transpedicular approach in lateral view, and FIG. 5 shows asingle transpedicular approach in coronal view. As FIG. 4 shows, theaccess portal 43 for a transpedicular approach enters at the top of thevertebral body 26, where the pedicle 42 is relatively thin, and extendsat an angle downward toward the bottom of the vertebral structure 26 toenter the interior volume 30. The catheter tube 12 carrying theexpandable structure 20 is guided into the interior volume 30 through anouter guide sheath 24, which passes through the portal 43.

As FIG. 6, expansion of the structure 20 in the interior volume 30compresses the cancellous bone 32 and creates an interior cavity 34. Thecavity 34 remains after collapse and removal of the structure 20 fromthe interior volume 30. The cavity 34 is intended to receive a fillingmaterial, like bone cement, to provide renewed interior structuralsupport for surrounding cortical bone 28. The compaction of cancellousbone also exerts interior force upon cortical bone 28, making itpossible to elevate or push broken and compressed bone back to or nearits original prefracture, or other desired, condition.

Access to the interior volume 30 of a given vertebral body 26 can beachieved through the sides of the body, shown in phantom lines 45 inFIG. 5. This approach is called a postero-lateral approach.

The above described access can be carried out in a minimally invasivemanner. It can also be carried out using an open surgical procedure.Using open surgery, the physician can approach the bone to be treated asif the procedure is percutaneous, except that there is no skin and othertissues between the surgeon and the bone being treated. This keeps thecortical bone as intact as possible, and can provide more freedom inaccessing the interior volume 30 of the vertebral body.

A. Representative Embodiments of Expandable Structures to TreatVertebrae

i. Constrained Donut-Shaped Geometries

FIG. 7 shows a representative embodiment of an expandable structure,which is broadly denoted by the numeral 210. The structure 210 comprisesa pair of hollow, inflatable, non-expandable parts 212 and 214 offlexible material, such as PET or Kevlar. Parts 212 and 214 have asuction tube 216 therebetween for drawing fats and other debris bysuction into tube 216 for transfer to a remote disposal location. Thesuction tube 216 has one or more suction holes so that suction may beapplied to the open end of tube 216 from a suction source (not shown).

The parts 212 and 214 are connected together by an adhesive which can beof any suitable type. Parts 212 and 214 are doughnut-shaped, as shown inFIG. 7, and have tubes 218 and 220 which communicate with and extendaway from the parts 212 and 214, respectively, to a source of inflatingliquid under pressure (not shown). The liquid expands the structure 210.

FIG. 8 shows a modified doughnut shape structure 280 of the type shownin FIG. 7, except the doughnut shapes of structure 280 are not stitchedonto one another. In FIG. 8, structure 280 has a pear-shaped outerconvex surface 282 which is made up of a first hollow part 284 and asecond hollow part 285. A tube 288 is provided for directing liquid intothe two parts along branches 290 and 292 to inflate the parts after theparts have been inserted into the interior volume of a bone. A cathetertube 216 may or may not be inserted into the space 296 between two partsof the balloon 280 to provide irrigation or suction. An adhesive bondsthe two parts 284 and 285 together.

FIG. 9 shows another representative embodiment of an expandablestructure, designated 309. The structure 309 has a generally roundgeometry and three expandable structure units 310, 312 and 314. Thestructure units 310, 312, and 314 include string-like externalrestraints 317, which limit the expansion of the structure units 310,312, and 314 in a direction transverse to the longitudinal axes of thestructure units 310, 312, and 314. The restraints 317 are made of thesame or similar material as that of the structure units 310, 312, and314, so that they have some resilience but substantially no expansioncapability.

A tubes 315 direct liquid under pressure into the structure units 310,312 and 314 to expand the units and cause compaction of cancellous bone.The restraints 317 limit expansion of the structure units prior tofailure, keeping the opposed sides 377 and 379 substantially flat andparallel with each other.

ii. Constrained Kidney-Shaped Geometries

FIG. 10 shows another representative embodiment of an expandablestructure 230, which has a kidney-shaped geometry. The structure 230 hasa pair of opposed kidney-shaped side walls 232 and a continuous end wall234. A tube 238 directs liquid into the structure to expand it withinthe vertebral structure.

FIG. 11 shows another representative embodiment of an expandablestructure 242, which also has a kidney-shaped geometry. The structure242 is initially a single chamber bladder, but the bladder is brandedalong curved lines or strips 241 to form attachment lines 244 which takethe shape of side-by-side compartments 246, as shown in FIG. 12. Asimilar pattern of strips as in 242, but in straight lines would beapplied to a structure that is square or rectangular. The brandingcauses a welding of the two sides of the bladder to occur.

The details of these and other expandable structures usable to treatvertebral bodies are described in U.S. patent application Ser. No.08/188,224, filed Jan. 26, 1994, and U.S. patent application Ser. No.08/871,114, filed Jun. 9, 1997, which are incorporated herein byreference.

B. Selection of Desired Geometry

The eventual selection of the size and shape of a particular expandablestructure 20 or structures to treat a targeted vertebral structure 26 isbased upon several factors. When multiple expandable bodies are used,the total combined dimensions of all expandable bodies deployed, whensubstantially expanded, should be taken into account.

The anterior-posterior (A-P) dimension (see FIG. 13) for the expandablestructure or bodies is selected from the CT scan or plain film or x-rayviews of the targeted vertebral structure 26. The A-P dimension ismeasured from the internal cortical wall of the anterior cortex to theinternal cortical wall of the posterior cortex of the vertebralstructure. In general, the appropriate A-P dimension for the expandablestructure or bodies is less than this anatomic measurement.

The appropriate side to side dimension L (see FIG. 13) for an expandablestructure or bodies is also selected from the CT scan, or from a plainfilm or x-ray view of the targeted vertebral structure. The side to sidedistance is measured between the internal cortical walls laterallyacross the targeted vertebral structure. In general, the appropriateside to side dimension L for the expandable structure is less than thisanatomic measurement.

The lumbar vertebral structure tends to be much wider in side to sidedimension L then in A-P dimension. In thoracic vertebral bodies, theside to side dimension and the A-P dimensions are almost equal.

The height dimensions H of the expandable structure or bodies (see FIG.13) is chosen by the CT scan or x-ray views of the vertebral bodiesabove and below the vertebral structure to be treated. The height of thevertebral bodies above and below the vertebral structure to be treatedare measured and averaged. This average is used to determine theappropriate height dimension of the chosen expandable structure.

The dimensions of expandable structure or bodies for use in vertebraeare patient specific and will vary across a broad range, as summarizedin the following table: Posterior Height (H) (A-P) Side to SideDimension Dimension Dimension (L) of Typical of Typical of TypicalExpandable Expandable Expandable Vertebra structure Structure StructureType or Bodies or Bodies or Bodies Lumbar 0.5 cm to 0.5 cm to 0.5 cm to4.0 cm 4.0 cm 5.0 cm Thoracic 0.5 cm to 0.5 cm to 0.5 cm to 3.5 cm 3.5cm 4.0 cm

A preferred expandable structure for use in a vertebral structure isstacked with two or more expandable members of unequal height(designated 20A and 20B in FIG. 13), where each member can be separatelyinflated through independent tube systems. The total height of the stackwhen fully inflated should be within the height ranges specified above.Such a design allows the fractured vertebral structure to be returned toits original height in steps, which can be easier on the surroundingtissue, and it also allows the same balloon to be used in a wider rangeof vertebral structure sizes.

III. Treatment of Other Bones

Like vertebrae, the interior regions of other bones in the appendicularskeleton are substantially occupied by cancellous bone, and thus can betreated with the use of one or more expandable structures. Regions inthe appendicular skeleton which can be treated using expandablestructures include the distal radius, the proximal tibial plateau, theproximal humerus, the proximal femoral head, and the calcaneus.

As for vertebral bodies, expandable structures possess the importantattribute of being able, in the course of forming cavities bycompressing cancellous bone, to also elevate or push broken orcompressed cortical bone back to or near its normal anatomic position.This is a particularly important attribute for the successful treatmentof compression fractures or cancellous bone fractures in theappendicular skeleton, such as the distal radius, the proximal humerus,the tibial plateau, the femoral head, hip, and calcaneus.

One representative example of an expandable structure for the treatmentof cancellous bone regions of a long bone (distal radius) will bedescribed.

A. Expandable Structure for the Distal Radius

The selection of an appropriate expandable to treat a fracture of thedistal radius will depend on the radiological size of the distal radiusand the location of the fracture.

FIGS. 14 and 15 show a representative expandable structure 260 for usein the distal radius. The structure 260, which is shown deployed in thedistal radius 252, has a shape which approximates a pyramid but moreclosely can be considered the shape of a humpbacked banana. The geometryof the structure 260 substantially fills the interior of the space ofthe distal radius to compact cancellous bone 254 against the innersurface 256 of cortical bone 258.

The structure 260 has a lower, conical portion 259 which extendsdownwardly into the hollow space of the distal radius 252. This conicalportion 259 increases in cross section as a central distal portion 261is approached. The cross section of the structure 260 is shown at acentral location (FIG. 14), which is near the widest location of thestructure 260. The upper end of the structure 260, denoted by thenumeral 262, converges to the catheter tube 288 for directing a liquidinto the structure 260 to expand it and force the cancellous boneagainst the inner surface of the cortical bone.

The shape of the structure 260 is determined and restrained by tuftsformed by string restraints 265. These restraints are optional andprovide additional strength to the structure 260, but are not requiredto achieve the desired configuration.

The structure 260 is placed into and taken out of the distal radius inthe same manner as that described above with respect to the vertebralbone.

Typical dimensions of the distal radius structure vary as follows:

The proximal end of the structure 260 (i.e. the part nearest the elbow)is cylindrical in shape and will vary from 0.4×0.4 cm to 1.8×1.8 cm.

The length of the distal radius structure will vary from 1.0 cm to 12.0cm.

The widest medial to lateral dimension of the distal radius structure,which occurs at or near the distal radio-ulnar joint, will measure from0.5 cm to 2.5 cm.

The distal anterior-posterior dimension of the distal radius structurewill vary from 0.4 to 3.0 cm.

The details of these and other expandable structures usable to treatvertebral bodies are described in U.S. patent application Ser. No.08/188,224, filed Jan. 26, 1994, and U.S. patent application Ser. No.08/871,114, filed Jun. 9, 1997, which are incorporated herein byreference.

IV. Deflection of an Expandable Structure

As FIG. 16 shows, a selected expandable structure 604 can include anenclosed tube 600, which provides an interior lumen 602 passing withinthe expandable structure 604. The lumen 602 accommodates the passage ofa stiffening member or stylet 606 made, e.g., from stainless steel ormolded plastic material.

The presence of the stylet 606 serves to keep the structure 604 in thedesired distally straightened condition during passage through anassociated guide sheath 608 toward the targeted body region 610, as FIG.16 shows. As before explained, access to the targeted body region 610through the guide sheath 608 can be accomplished using a closed,minimally invasive procedure or with an open procedure.

As shown in FIG. 17, the stylet 606 can have a preformed memory, tonormally bend the distal region 612 of the stylet 606. The memory isovercome to straighten the stylet 606 when confined within the guidesheath 608, as FIG. 16 shows. However, as the structure 604 and stylet606 advance free of the guide sheath 608 and pass into the targetedregion 610, the preformed memory bends the distal stylet region 612. Thebend of the distal stylet region 612 bends the tube 600 and therebyshifts the axis 614 of the attached expandable structure 604 relative tothe axis 616 of the access path (i.e., the guide sheath 608). Theprebent stylet 606, positioned within the interior of the structure 604,aids in altering the geometry of the structure 604 in accordance withthe orientation desired when the structure 604 is deployed for use inthe targeted region 610.

V. Single Use

Expansion of any one of the expandable structures described hereinduring first use in a targeted structure region generates stress on thematerial or materials which make up the structure. The material stresscreated by operational loads during first use in a targeted structureregion can significantly alter the molded morphology of the structure,making future performance of the structure unpredictable.

For example, expansion within bone during a single use creates contactwith surrounding cortical and cancellous bone. This contact can damagethe structure, creating localized regions of weakness, which may escapedetection. The existence of localized regions of weakness canunpredictably cause overall structural failure during a subsequent use.

In addition, exposure to blood and tissue during a single use can entrapbiological components on or within the structure or the associatedcatheter tube. Despite cleaning and subsequent sterilization, thepresence of entrapped biological components can lead to unacceptablepyrogenic reactions.

As a result, following first use, the structure can not be relied uponto reach its desired configuration during subsequent use and may nototherwise meet established performance and sterilization specifications.The effects of material stress and damage caused during a single use,coupled with the possibility of pyrogen reactions even afterresterilization, reasonably justify imposing a single use restrictionupon devices which carry these expandable structures for deployment inbone.

To protect patients from the potential adverse consequences occasionedby multiple use, which include disease transmission, or material stressand instability, or decreased or unpredictable performance, theinvention also provides a kit 500 (see FIGS. 18 and 19) for storing asingle use probe 502, which carries an expandable structure 504described herein prior to deployment in bone.

In the illustrated embodiment (see FIGS. 18 and 19), the kit 500includes an interior tray 508. The tray 508 holds the probe 502 in alay-flat, straightened condition during sterilization and storage priorto its first use. The tray 508 can be formed from die cut cardboard orthermoformed plastic material. The tray 508 includes one or more spacedapart tabs 510, which hold the catheter tube 503 and expandablestructure 504 in the desired lay-flat, straightened condition. As shown,the facing ends of the tabs 510 present a nesting, serpentine geometry,which engages the catheter tube 503 essentially across its entire width,to securely retain the catheter tube 503 on the tray 508.

The kit 500 includes an inner wrap 512, which is peripherally sealed byheat or the like, to enclose the tray 508 from contact with the outsideenvironment. One end of the inner wrap 512 includes a conventionalpeal-away seal 514 (see FIG. 19), to provide quick access to the tray508 upon instance of use, which preferably occurs in a sterileenvironment, such as within an operating room.

The kit 500 also includes an outer wrap 516, which is also peripherallysealed by heat or the like, to enclosed the inner wrap 512. One end ofthe outer wrap 516 includes a conventional peal-away seal 518 (see FIG.19), to provide access to the inner wrap 512, which can be removed fromthe outer wrap 516 in anticipation of imminent use of the probe 502,without compromising sterility of the probe 502 itself.

Both inner and outer wraps 512 and 516 (see FIG. 19) each includes aperipherally sealed top sheet 520 and bottom sheet 522. In theillustrated embodiment, the top sheet 520 is made of transparent plasticfilm, like polyethylene or MYLAR™ material, to allow visualidentification of the contents of the kit 500. The bottom sheet 522 ismade from a material that is permeable to EtO sterilization gas, e.g.,TYVEC™ plastic material (available from DuPont).

The sterile kit 500 also carries a label or insert 506, which includesthe statement “For Single Patient Use Only” (or comparable language) toaffirmatively caution against reuse of the contents of the kit 500. Thelabel 506 also preferably affirmatively instructs againstresterilization of the probe 502. The label 506 also preferablyinstructs the physician or user to dispose of the probe 502 and theentire contents of the kit 500 upon use in accordance with applicablebiological waste procedures.

The presence of the probe 502 packaged in the kit 500 verifies to thephysician or user that probe 502 is sterile and has not be subjected toprior use. The physician or user is thereby assured that the expandablestructure 504 meets established performance and sterilityspecifications, and will have the desired configuration when expandedfor use.

The features of the invention are set forth in the following claims.

1. A method comprising selecting a bone for treatment having a corticalwall enclosing a cancellous bone volume, providing a void creationdevice including an expandable structure adapted to undergo expansion inthe cancellous bone volume, the expandable structure having at least onedimension so that the expandable structure will assume a predeterminedshape and size when substantially expanded that compacts only a firstvolume of the cancellous bone volume to form a void, leaving a secondvolume of the cancellous bone volume substantially uncompacted by theexpandable structure, introducing the void creation device into the bonethrough a percutaneous access path, expanding the expandable structurein the cancellous bone volume to the predetermined shape and size tocreate the void, leaving the second volume of the cancellous bone volumesubstantially uncompacted by the expandable structure, and placing afilling material within the void through the percutaneous access path.2. A method according to claim 1 wherein the first volume of thecancellous bone volume comprises about 30% to 90% of the cancellous bonevolume.
 3. A method according to claim 1 wherein the first volume of thecancellous bone volume comprises about 40% to 90% of the cancellous bonevolume.
 4. A method according to claim 1 wherein the structure comprisesan inflatable body.
 5. A method according to claim 1 wherein thestructure comprises a balloon.
 6. A method according to claim 1 whereinthe filling material placed within the void hardens within the void. 7.A method according to claim 1 further including removing the structurefrom the void.